There are certain biological formations that can help deliver drugs or genetic materials to cells–liposomes, for instance, have medicine or genetic material encapsulated in them, and they can either be absorbed into a cell or join with the cell membrane to release their cargo. Also, dendrimers are tree-like protein polymer structures that form “pockets” within them, and the medicine or genetic material is deposited into the pockets and delivered directly to the tumor or organ that needs them. These treatments are specifically targeted at the necessary cells, similar to radiation or chemotherapy in cancer treatment. They would be injected or delivered directly to the site. I would say that a source to start with would be the book we used as our beginning textbook in my nano program. It includes many other sources for continuing research into the subject.